The studies proposed are aimed at understanding the control of the phosphorylation of membrane proteins in the human erythrocyte, as well as the functional significance of the modifications in the structure and function of the membrane. Particular interest is in the phosphorylation of spectrin. The major membrane protein disposed in a fibrillar array as the inner surface of the membrane, whose interactions with actin, ATP and divalent cations appears to determine, in part, erythrocyte shape and deformability. Spectrin is the predominant phosphoprotein in the erythrocyte, and its phosphorylation is mediated by a cAMP-independent protein kinase. The isolation of this enzyme, as well as spectrin phosphatase, their characterization, and the modes of regulation of their activity are the major goals of the current work.